Improvements in wireless communications, as well as multimedia applications and hardware, have accelerated the emergence of fourth generation (4G) wireless systems. The primary expectation from all future 4G systems is that they provide extremely high data rates to an very large number of users at the same time. 4G will likely be based on Orthogonal Frequency-Division Multiplexing (OFDM). Worldwide Interoperability for Microwave Access (WiMAX), an OFDM technology, is a suitable candidate for 4G. WiMAX has the potential ability to satisfy challenging throughput and capacity needs and, more importantly, the capacity of WiMAX systems can be improved further by adding Multiple-Input Multiple-Output (MIMO) feature. Because MIMO can considerably enhance the potential of WiMAX systems, it has been made part of the IEEE 802.16 and 802.16e standards.
Systems with MIMO capability operate on a number of parallel channels, which leads to a multiplexing gain. In MIMO systems, at the expense of increased hardware and computational complexity, a high spectral efficiency can be achieved. Part of the increase in hardware and computational complexity is due to the need for multiple transmitters and receivers. The number of receivers has to equal the number of transmitters. The spectral efficiency, which can be utilized as data rate, capacity, or coverage improvement, makes the MIMO technology attractive for bandwidth-greedy wireless applications. Reliable MIMO-OFDM system design requires performing certain MIMO measurements on the system. Optimally, these measurements would be performed by either using multiple Vector Signal Analyzers (VSAs) or a single VSA with multiple input branches. However, this type of measurement setup is very costly.